(1) Field of the Invention
The present invention relates to a display device for a vehicle, in which (a) a virtual image of an image projected on a projection area of a windshield of the vehicle, onto which area the image displayed on a display source is reflected by a reflecting mirror and (b) a front view of the vehicle to be seen from an eye point of the vehicle through the windshield are seen in a superimposed manner.
(2) Description of the Related Art
Recently, accompanied with increment and diversification of information required by a driver during a drive of a vehicle, in order to improve visibility, a projection type display device for a vehicle being called a head up display device (HUD device) has been adopted, in which an image is displayed as a virtual image thereof on a windshield of the vehicle and subjected to be seen by the driver in a superimposed manner together with a front view of the vehicle through the windshield (see Japanese Patent Applications Laid-Open No. H2-164621, H3-209210, H8-85363, 2000-187181, 2004-219859, and 2005-156678).
In FIG. 4, a display device 10 for a vehicle is manufactured as a unit receiving a display source 11 and a reflecting member 12 in a device body 10a of the display device 10. The display device 10 is arranged at the most suitable position depending upon conditions such as a position of an eye point EP of a driver of the vehicle, a display position (or distance) of a virtual image S, and attaching position and angle of a windshield 3 with respect to the vehicle.
However, in the vehicle, there may be no room for placing the display device 10 because of a vehicle body, duct, and reinforcing member, therefore when trying to place the display device 10 at the best position, a part of the device body 10a may interfere with a vehicle body 4 (particularly, with a cowl) as shown in FIG. 4, causing the placement of the display device 10 to be difficult physically.
For example, as shown in FIG. 5A, the device body 10a may be placed at a location such as the rear of the vehicle indicated an arrow X shown in FIG. 5A where there is a room in the vehicle. However, in such a case, since the display light from the display source 11 reflected by the reflecting member 12 is shifted from an original reflection point P1 on the windshield 3, therefore the virtual image S is shifted by a gap ΔP from the best display position P10 to a display position P11. When the gap ΔP is large, the virtual image S cannot be seen from the eye point EP and therefore, the device body 10a of the display device 10 cannot be placed at such a position.
Further, as shown in FIG. 5B, when the device body 10a is moved along an optical axis A toward the upper part Y of the vehicle, it is indeed possible to remove the problem that the display light is shifted from an original reflection point P1 on the windshield 3, however, there is a new problem that such a placement of the device body 10a may obstruct the front field of vision depending upon the condition of the vehicle. Furthermore, when a prism or the like for adjusting the light reflected by the reflecting member toward the reflection point P1 in order to remove the above problem, there is a new problem that external light such as sun light may be reflected by the prism so as to be transferred onto the windshield.
Moreover, in the HUD device described in the Japanese Patent Applications Laid-Open No. H8-85363 and 2005-156678, the display light is reflected toward the eye point by a combiner instead of the windshield, therefore there is no problem that the display light is shifted from the reflection point due to the placement of the display device. However, as for the HUD device, since a position where the combiner is placed is limited, therefore a position where the HUD device is attached cannot be altered. Accordingly, the display device cannot be mounted on the vehicle when things come to the worst depending upon an attachment limiting condition of the vehicle.